I am a huge fan of mailermailer.
They do have the signup form you ask about, you get to use them free until you have 200 recipients, then the cost is graduated and reasonable.
I have used them for 4 years now without complaints. The have the most extensive stats of anyone, and you can drill down and see exactly who clicks on what and customize mailings to fit the recipient perfectly.
Geez, I have said this so often now, I should see about getting them to pay me. :tounge2: